diff --git a/lib/Transforms/IPO/MergeFunctions.cpp b/lib/Transforms/IPO/MergeFunctions.cpp
index 17bc2d41a4c..16083ec7817 100644
--- a/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/lib/Transforms/IPO/MergeFunctions.cpp
@@ -9,10 +9,6 @@
 //
 // This pass looks for equivalent functions that are mergable and folds them.
 //
-// A Function will not be analyzed if:
-// * it is overridable at runtime (except for weak linkage), or
-// * it is used by anything other than the callee parameter of a call/invoke
-//
 // A hash is computed from the function, based on its type and number of
 // basic blocks.
 //
@@ -24,8 +20,6 @@
 // When a match is found, the functions are folded. We can only fold two
 // functions when we know that the definition of one of them is not
 // overridable.
-// * fold a function marked internal by replacing all of its users.
-// * fold extern or weak functions by replacing them with a global alias
 //
 //===----------------------------------------------------------------------===//
 //
@@ -48,6 +42,7 @@
 #define DEBUG_TYPE "mergefunc"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Constants.h"
 #include "llvm/InlineAsm.h"
@@ -62,7 +57,6 @@
 using namespace llvm;
 
 STATISTIC(NumFunctionsMerged, "Number of functions merged");
-STATISTIC(NumMergeFails, "Number of identical function pairings not merged");
 
 namespace {
   struct VISIBILITY_HIDDEN MergeFunctions : public ModulePass {
@@ -81,16 +75,168 @@ ModulePass *llvm::createMergeFunctionsPass() {
   return new MergeFunctions();
 }
 
+// ===----------------------------------------------------------------------===
+// Comparison of functions
+// ===----------------------------------------------------------------------===
+
 static unsigned long hash(const Function *F) {
-  return F->size() ^ reinterpret_cast<unsigned long>(F->getType());
-  //return F->size() ^ F->arg_size() ^ F->getReturnType();
+  const FunctionType *FTy = F->getFunctionType();
+
+  FoldingSetNodeID ID;
+  ID.AddInteger(F->size());
+  ID.AddInteger(F->getCallingConv());
+  ID.AddBoolean(F->hasGC());
+  ID.AddBoolean(FTy->isVarArg());
+  ID.AddInteger(FTy->getReturnType()->getTypeID());
+  for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
+    ID.AddInteger(FTy->getParamType(i)->getTypeID());
+  return ID.ComputeHash();
+}
+
+/// IgnoreBitcasts - given a bitcast, returns the first non-bitcast found by
+/// walking the chain of cast operands. Otherwise, returns the argument.
+static Value* IgnoreBitcasts(Value *V) {
+  while (BitCastInst *BC = dyn_cast<BitCastInst>(V))
+    V = BC->getOperand(0);
+
+  return V;
+}
+
+/// isEquivalentType - any two pointers are equivalent. Otherwise, standard
+/// type equivalence rules apply.
+static bool isEquivalentType(const Type *Ty1, const Type *Ty2) {
+  if (Ty1 == Ty2)
+    return true;
+  if (Ty1->getTypeID() != Ty2->getTypeID())
+    return false;
+
+  switch(Ty1->getTypeID()) {
+  case Type::VoidTyID:
+  case Type::FloatTyID:
+  case Type::DoubleTyID:
+  case Type::X86_FP80TyID:
+  case Type::FP128TyID:
+  case Type::PPC_FP128TyID:
+  case Type::LabelTyID:
+  case Type::MetadataTyID:
+    return true;
+
+  case Type::IntegerTyID:
+  case Type::OpaqueTyID:
+    // Ty1 == Ty2 would have returned true earlier.
+    return false;
+
+  default:
+    assert(0 && "Unknown type!");
+    return false;
+
+  case Type::PointerTyID: {
+    const PointerType *PTy1 = cast<PointerType>(Ty1);
+    const PointerType *PTy2 = cast<PointerType>(Ty2);
+    return PTy1->getAddressSpace() == PTy2->getAddressSpace();
+  }
+
+  case Type::StructTyID: {
+    const StructType *STy1 = cast<StructType>(Ty1);
+    const StructType *STy2 = cast<StructType>(Ty2);
+    if (STy1->getNumElements() != STy2->getNumElements())
+      return false;
+
+    if (STy1->isPacked() != STy2->isPacked())
+      return false;
+
+    for (unsigned i = 0, e = STy1->getNumElements(); i != e; ++i) {
+      if (!isEquivalentType(STy1->getElementType(i), STy2->getElementType(i)))
+        return false;
+    }
+    return true;
+  }
+
+  case Type::FunctionTyID: {
+    const FunctionType *FTy1 = cast<FunctionType>(Ty1);
+    const FunctionType *FTy2 = cast<FunctionType>(Ty2);
+    if (FTy1->getNumParams() != FTy2->getNumParams() ||
+        FTy1->isVarArg() != FTy2->isVarArg())
+      return false;
+
+    if (!isEquivalentType(FTy1->getReturnType(), FTy2->getReturnType()))
+      return false;
+
+    for (unsigned i = 0, e = FTy1->getNumParams(); i != e; ++i) {
+      if (!isEquivalentType(FTy1->getParamType(i), FTy2->getParamType(i)))
+        return false;
+    }
+    return true;
+  }
+
+  case Type::ArrayTyID:
+  case Type::VectorTyID: {
+    const SequentialType *STy1 = cast<SequentialType>(Ty1);
+    const SequentialType *STy2 = cast<SequentialType>(Ty2);
+    return isEquivalentType(STy1->getElementType(), STy2->getElementType());
+  }
+  }
+}
+
+/// isEquivalentOperation - determine whether the two operations are the same
+/// except that pointer-to-A and pointer-to-B are equivalent. This should be
+/// kept in sync with Instruction::isSameOperandAs.
+static bool isEquivalentOperation(const Instruction *I1, const Instruction *I2) {
+  if (I1->getOpcode() != I2->getOpcode() ||
+      I1->getNumOperands() != I2->getNumOperands() ||
+      !isEquivalentType(I1->getType(), I2->getType()))
+    return false;
+
+  // We have two instructions of identical opcode and #operands.  Check to see
+  // if all operands are the same type
+  for (unsigned i = 0, e = I1->getNumOperands(); i != e; ++i)
+    if (!isEquivalentType(I1->getOperand(i)->getType(),
+                          I2->getOperand(i)->getType()))
+      return false;
+
+  // Check special state that is a part of some instructions.
+  if (const LoadInst *LI = dyn_cast<LoadInst>(I1))
+    return LI->isVolatile() == cast<LoadInst>(I2)->isVolatile() &&
+           LI->getAlignment() == cast<LoadInst>(I2)->getAlignment();
+  if (const StoreInst *SI = dyn_cast<StoreInst>(I1))
+    return SI->isVolatile() == cast<StoreInst>(I2)->isVolatile() &&
+           SI->getAlignment() == cast<StoreInst>(I2)->getAlignment();
+  if (const CmpInst *CI = dyn_cast<CmpInst>(I1))
+    return CI->getPredicate() == cast<CmpInst>(I2)->getPredicate();
+  if (const CallInst *CI = dyn_cast<CallInst>(I1))
+    return CI->isTailCall() == cast<CallInst>(I2)->isTailCall() &&
+           CI->getCallingConv() == cast<CallInst>(I2)->getCallingConv() &&
+           CI->getAttributes().getRawPointer() ==
+             cast<CallInst>(I2)->getAttributes().getRawPointer();
+  if (const InvokeInst *CI = dyn_cast<InvokeInst>(I1))
+    return CI->getCallingConv() == cast<InvokeInst>(I2)->getCallingConv() &&
+           CI->getAttributes().getRawPointer() ==
+             cast<InvokeInst>(I2)->getAttributes().getRawPointer();
+  if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(I1)) {
+    if (IVI->getNumIndices() != cast<InsertValueInst>(I2)->getNumIndices())
+      return false;
+    for (unsigned i = 0, e = IVI->getNumIndices(); i != e; ++i)
+      if (IVI->idx_begin()[i] != cast<InsertValueInst>(I2)->idx_begin()[i])
+        return false;
+    return true;
+  }
+  if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(I1)) {
+    if (EVI->getNumIndices() != cast<ExtractValueInst>(I2)->getNumIndices())
+      return false;
+    for (unsigned i = 0, e = EVI->getNumIndices(); i != e; ++i)
+      if (EVI->idx_begin()[i] != cast<ExtractValueInst>(I2)->idx_begin()[i])
+        return false;
+    return true;
+  }
+
+  return true;
 }
 
 static bool compare(const Value *V, const Value *U) {
   assert(!isa<BasicBlock>(V) && !isa<BasicBlock>(U) &&
          "Must not compare basic blocks.");
 
-  assert(V->getType() == U->getType() &&
+  assert(isEquivalentType(V->getType(), U->getType()) &&
         "Two of the same operation have operands of different type.");
 
   // TODO: If the constant is an expression of F, we should accept that it's
@@ -117,18 +263,24 @@ static bool compare(const Value *V, const Value *U) {
 static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
                    DenseMap<const Value *, const Value *> &ValueMap,
                    DenseMap<const Value *, const Value *> &SpeculationMap) {
-  // Specutively add it anyways. If it's false, we'll notice a difference later, and
-  // this won't matter.
+  // Speculatively add it anyways. If it's false, we'll notice a difference
+  // later, and this won't matter.
   ValueMap[BB1] = BB2;
 
   BasicBlock::const_iterator FI = BB1->begin(), FE = BB1->end();
   BasicBlock::const_iterator GI = BB2->begin(), GE = BB2->end();
 
   do {
-    if (!FI->isSameOperationAs(const_cast<Instruction *>(&*GI)))
-      return false;
+    if (isa<BitCastInst>(FI)) {
+      ++FI;
+      continue;
+    }
+    if (isa<BitCastInst>(GI)) {
+      ++GI;
+      continue;
+    }
 
-    if (FI->getNumOperands() != GI->getNumOperands())
+    if (!isEquivalentOperation(FI, GI))
       return false;
 
     if (ValueMap[FI] == GI) {
@@ -140,8 +292,8 @@ static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
       return false;
 
     for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
-      Value *OpF = FI->getOperand(i);
-      Value *OpG = GI->getOperand(i);
+      Value *OpF = IgnoreBitcasts(FI->getOperand(i));
+      Value *OpG = IgnoreBitcasts(GI->getOperand(i));
 
       if (ValueMap[OpF] == OpG)
         continue;
@@ -149,10 +301,8 @@ static bool equals(const BasicBlock *BB1, const BasicBlock *BB2,
       if (ValueMap[OpF] != NULL)
         return false;
 
-      assert(OpF->getType() == OpG->getType() &&
-             "Two of the same operation has operands of different type.");
-
-      if (OpF->getValueID() != OpG->getValueID())
+      if (OpF->getValueID() != OpG->getValueID() ||
+          !isEquivalentType(OpF->getType(), OpG->getType()))
         return false;
 
       if (isa<PHINode>(FI)) {
@@ -203,14 +353,15 @@ static bool equals(const Function *F, const Function *G) {
   if (F->hasSection() && F->getSection() != G->getSection())
     return false;
 
+  if (F->isVarArg() != G->isVarArg())
+    return false;
+
   // TODO: if it's internal and only used in direct calls, we could handle this
   // case too.
   if (F->getCallingConv() != G->getCallingConv())
     return false;
 
-  // TODO: We want to permit cases where two functions take T* and S* but
-  // only load or store them into T** and S**.
-  if (F->getType() != G->getType())
+  if (!isEquivalentType(F->getFunctionType(), G->getFunctionType()))
     return false;
 
   DenseMap<const Value *, const Value *> ValueMap;
@@ -237,88 +388,198 @@ static bool equals(const Function *F, const Function *G) {
   return true;
 }
 
-static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
-  if (FnVec[i]->mayBeOverridden() && !FnVec[j]->mayBeOverridden())
-    std::swap(FnVec[i], FnVec[j]);
+// ===----------------------------------------------------------------------===
+// Folding of functions
+// ===----------------------------------------------------------------------===
 
+// Cases:
+// * F is external strong, G is external strong:
+//   turn G into a thunk to F    (1)
+// * F is external strong, G is external weak:
+//   turn G into a thunk to F    (1)
+// * F is external weak, G is external weak:
+//   unfoldable
+// * F is external strong, G is internal:
+//   address of G taken:
+//     turn G into a thunk to F  (1)
+//   address of G not taken:
+//     make G an alias to F      (2)
+// * F is internal, G is external weak
+//   address of F is taken:
+//     turn G into a thunk to F  (1)
+//   address of F is not taken:
+//     make G an alias of F      (2)
+// * F is internal, G is internal:
+//   address of F and G are taken:
+//     turn G into a thunk to F  (1)
+//   address of G is not taken:
+//     make G an alias to F      (2)
+//
+// alias requires linkage == (external,local,weak) fallback to creating a thunk
+// external means 'externally visible' linkage != (internal,private)
+// internal means linkage == (internal,private)
+// weak means linkage mayBeOverridable
+// being external implies that the address is taken
+//
+// 1. turn G into a thunk to F
+// 2. make G an alias to F
+
+enum LinkageCategory {
+  ExternalStrong,
+  ExternalWeak,
+  Internal
+};
+
+static LinkageCategory categorize(const Function *F) {
+  switch (F->getLinkage()) {
+  case GlobalValue::InternalLinkage:
+  case GlobalValue::PrivateLinkage:
+    return Internal;
+
+  case GlobalValue::WeakAnyLinkage:
+  case GlobalValue::WeakODRLinkage:
+  case GlobalValue::ExternalWeakLinkage:
+    return ExternalWeak;
+
+  case GlobalValue::ExternalLinkage:
+  case GlobalValue::AvailableExternallyLinkage:
+  case GlobalValue::LinkOnceAnyLinkage:
+  case GlobalValue::LinkOnceODRLinkage:
+  case GlobalValue::AppendingLinkage:
+  case GlobalValue::DLLImportLinkage:
+  case GlobalValue::DLLExportLinkage:
+  case GlobalValue::GhostLinkage:
+  case GlobalValue::CommonLinkage:
+    return ExternalStrong;
+  }
+
+  assert(0 && "Unknown LinkageType.");
+  return ExternalWeak;
+}
+
+static void ThunkGToF(Function *F, Function *G) {
+  Function *NewG = Function::Create(G->getFunctionType(), G->getLinkage(),
+                                    "", G->getParent());
+  BasicBlock *BB = BasicBlock::Create("", NewG);
+
+  std::vector<Value *> Args;
+  unsigned i = 0;
+  const FunctionType *FFTy = F->getFunctionType();
+  for (Function::arg_iterator AI = NewG->arg_begin(), AE = NewG->arg_end();
+       AI != AE; ++AI) {
+    if (FFTy->getParamType(i) == AI->getType())
+      Args.push_back(AI);
+    else {
+      Value *BCI = new BitCastInst(AI, FFTy->getParamType(i), "", BB);
+      Args.push_back(BCI);
+    }
+    ++i;
+  }
+
+  CallInst *CI = CallInst::Create(F, Args.begin(), Args.end(), "", BB);
+  CI->setTailCall();
+  if (NewG->getReturnType() == Type::VoidTy) {
+    ReturnInst::Create(BB);
+  } else if (CI->getType() != NewG->getReturnType()) {
+    Value *BCI = new BitCastInst(CI, NewG->getReturnType(), "", BB);
+    ReturnInst::Create(BCI, BB);
+  } else {
+    ReturnInst::Create(CI, BB);
+  }
+
+  NewG->copyAttributesFrom(G);
+  NewG->takeName(G);
+  G->replaceAllUsesWith(NewG);
+  G->eraseFromParent();
+
+  // TODO: look at direct callers to G and make them all direct callers to F
+  // iff G->hasAddressTaken() is false.
+}
+
+static void AliasGToF(Function *F, Function *G) {
+  if (!G->hasExternalLinkage() && !G->hasLocalLinkage() && !G->hasWeakLinkage())
+    return ThunkGToF(F, G);
+
+  GlobalAlias *GA = new GlobalAlias(
+    G->getType(), G->getLinkage(), "",
+    ConstantExpr::getBitCast(F, G->getType()), G->getParent());
+  F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
+  GA->takeName(G);
+  GA->setVisibility(G->getVisibility());
+  G->replaceAllUsesWith(GA);
+  G->eraseFromParent();
+}
+
+static bool fold(std::vector<Function *> &FnVec, unsigned i, unsigned j) {
   Function *F = FnVec[i];
   Function *G = FnVec[j];
 
-  if (!F->mayBeOverridden()) {
-    if (G->hasLocalLinkage()) {
-      F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
-      G->replaceAllUsesWith(F);
-      G->eraseFromParent();
-      ++NumFunctionsMerged;
-      return true;
-    }
+  LinkageCategory catF = categorize(F);
+  LinkageCategory catG = categorize(G);
 
-    if (G->hasExternalLinkage() || G->hasWeakLinkage()) {
-      GlobalAlias *GA = new GlobalAlias(G->getType(), G->getLinkage(), "",
-                                        F, G->getParent());
-      F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
-      GA->takeName(G);
-      GA->setVisibility(G->getVisibility());
-      G->replaceAllUsesWith(GA);
-      G->eraseFromParent();
-      ++NumFunctionsMerged;
-      return true;
-    }
+  if (catF == ExternalWeak || (catF == Internal && catG == ExternalStrong)) {
+    std::swap(FnVec[i], FnVec[j]);
+    std::swap(F, G);
+    std::swap(catF, catG);
   }
 
-  if (F->hasWeakLinkage() && G->hasWeakLinkage()) {
-    GlobalAlias *GA_F = new GlobalAlias(F->getType(), F->getLinkage(), "",
-                                        0, F->getParent());
-    GA_F->takeName(F);
-    GA_F->setVisibility(F->getVisibility());
-    F->setAlignment(std::max(F->getAlignment(), G->getAlignment()));
-    F->replaceAllUsesWith(GA_F);
-    F->setName("folded." + GA_F->getName());
-    F->setLinkage(GlobalValue::ExternalLinkage);
-    GA_F->setAliasee(F);
+  switch (catF) {
+    case ExternalStrong:
+      switch (catG) {
+        case ExternalStrong:
+        case ExternalWeak:
+          ThunkGToF(F, G);
+          break;
+        case Internal:
+          if (G->hasAddressTaken())
+            ThunkGToF(F, G);
+          else
+            AliasGToF(F, G);
+          break;
+      }
+      break;
 
-    GlobalAlias *GA_G = new GlobalAlias(G->getType(), G->getLinkage(), "",
-                                        F, G->getParent());
-    GA_G->takeName(G);
-    GA_G->setVisibility(G->getVisibility());
-    G->replaceAllUsesWith(GA_G);
-    G->eraseFromParent();
+    case ExternalWeak:
+      return false;
 
-    ++NumFunctionsMerged;
-    return true;
+    case Internal:
+      switch (catG) {
+        case ExternalStrong:
+          assert(0);
+          // fall-through
+        case ExternalWeak:
+	  if (F->hasAddressTaken())
+            ThunkGToF(F, G);
+          else
+            AliasGToF(F, G);
+	  break;
+        case Internal: {
+          bool addrTakenF = F->hasAddressTaken();
+          bool addrTakenG = G->hasAddressTaken();
+          if (!addrTakenF && addrTakenG) {
+            std::swap(FnVec[i], FnVec[j]);
+            std::swap(F, G);
+	    std::swap(addrTakenF, addrTakenG);
+	  }
+
+          if (addrTakenF && addrTakenG) {
+            ThunkGToF(F, G);
+          } else {
+            assert(!addrTakenG);
+            AliasGToF(F, G);
+          }
+	} break;
+      }
+      break;
   }
 
-  DOUT << "Failed on " << F->getName() << " and " << G->getName() << "\n";
-
-  ++NumMergeFails;
-  return false;
+  ++NumFunctionsMerged;
+  return true;
 }
 
-static bool hasAddressTaken(User *U) {
-  for (User::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I) {
-    User *Use = *I;
-
-    // 'call (bitcast @F to ...)' happens a lot.
-    while (isa<ConstantExpr>(Use) && Use->hasOneUse()) {
-      Use = *Use->use_begin();
-    }
-
-    if (isa<ConstantExpr>(Use)) {
-      if (hasAddressTaken(Use))
-        return true;
-    }
-
-    if (!isa<CallInst>(Use) && !isa<InvokeInst>(Use))
-      return true;
-
-    // Make sure we aren't passing U as a parameter to call instead of the
-    // callee.
-    if (CallSite(cast<Instruction>(Use)).hasArgument(U))
-      return true;
-  }
-
-  return false;
-}
+// ===----------------------------------------------------------------------===
+// Pass definition
+// ===----------------------------------------------------------------------===
 
 bool MergeFunctions::runOnModule(Module &M) {
   bool Changed = false;
@@ -329,25 +590,19 @@ bool MergeFunctions::runOnModule(Module &M) {
     if (F->isDeclaration() || F->isIntrinsic())
       continue;
 
-    if (!F->hasLocalLinkage() && !F->hasExternalLinkage() &&
-        !F->hasWeakLinkage())
-      continue;
-
-    if (hasAddressTaken(F))
-      continue;
-
     FnMap[hash(F)].push_back(F);
   }
 
-  // TODO: instead of running in a loop, we could also fold functions in callgraph
-  // order. Constructing the CFG probably isn't cheaper than just running in a loop.
+  // TODO: instead of running in a loop, we could also fold functions in
+  // callgraph order. Constructing the CFG probably isn't cheaper than just
+  // running in a loop, unless it happened to already be available.
 
   bool LocalChanged;
   do {
     LocalChanged = false;
+    DOUT << "size: " << FnMap.size() << "\n";
     for (std::map<unsigned long, std::vector<Function *> >::iterator
          I = FnMap.begin(), E = FnMap.end(); I != E; ++I) {
-      DOUT << "size: " << FnMap.size() << "\n";
       std::vector<Function *> &FnVec = I->second;
       DOUT << "hash (" << I->first << "): " << FnVec.size() << "\n";